Why two groups with same median shows significant difference when using Wilcoxon signed rank test or Mann-Whitney u test?

More Brijesh Sathian's questions See All

Can the antibodies that neutralize HIV would provide effective protection against the virus?

04 May 2017 5,797 3 View

Whether to replace p value by Confidence Interval?. or to believe on Sir Ronald A. Fisher ?

03 April 2016 5,684 15 View

What is Information and Communication Technology (ICT) in Health? What is the application?

10 November 2015 6,494 3 View

Is it necessary to do sample size calculation in cohort studies? If no, then why?

There are several cohort studies published in reputed journals without sample size calculation. Please share ideas on cohort studies then the budding researchers will get proper knowledge about...

08 September 2015 6,626 4 View

What is the quality difference in a print journal compared to e journal?

Recently, Medical Council of India made a dicision to not accept the manuscripts published in a e journal for the promotion of faculties in the medical colleges of India. Is it a wise dicision? Is...

08 September 2015 4,553 7 View

Is it scientifically true, whether the Collider at CERN was the reason behind Nepal earthquakes?

04 May 2015 4,038 3 View

How can earthquakes be predicted? Which statistical models work best?

04 May 2015 8,026 14 View

What is the reliability of the scientific information on the research done by email using Survey Monkey API online questionnaire?

04 May 2015 7,706 6 View

What is the difference between Incidence, Prevalence and Percentage ?

02 March 2015 4,718 6 View

Whether EMBASE should be considered as equivalent to PubMed Indexation?

02 March 2015 7,953 5 View

error in running a model in Abaqus

Excessive rotation of nodes in node set ErrNodeExcessRotation-Step1

17 August 2021 0 0 View

error in modelling model in Abaqus

Excessive rotation of nodes in node set ErrNodeExcessRotation-Step1

17 August 2021 0 0 View

MGL tools

20 June 2021 0 0 View

i have some problem with chtMultiRegionSimpleFoam

--> FOAM FATAL ERROR: Maximum number of iterations exceeded From function Foam::scalar Foam::species::thermo::T(Foam::scalar, Foam::scalar, Foam::scalar, Foam::scalar (Foam::species::thermo::*)(Foam::scalar, Foam::scalar) const, Foam::scalar (Foam::species::thermo::*)(Foam::scalar, Foam::scalar) const, Foam::scalar (Foam::species::thermo::*)(Foam::scalar) const) const [with Thermo = Foam::hConstThermo >; Type = Foam::sensibleEnthalpy; Foam::scalar = double; Foam::species::thermo = Foam::species::thermo >, Foam::sensibleEnthalpy>] in file /home/ubuntu/OpenFOAM/OpenFOAM-4.1/src/thermophysicalModels/specie/lnInclude/thermoI.H at line 66. FOAM aborting #0 Foam::error::printStack(Foam::Ostream&) at ??:? #1 Foam::error::abort() at ??:? #2 Foam::heRhoThermo >, Foam::sensibleEnthalpy> > > >::calculate() at ??:? #3 Foam::heRhoThermo >, Foam::sensibleEnthalpy> > > >::correct() at ??:? #4 ? at ??:? #5 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6" #6 ? at ??:?

24 March 2021 0 0 View

How to compare two groups with only two measurements?

Hiiiii everyone! I have an enquiry on statistical analysis. I was looking for many forum and it's still cannot solve my problem. I want to compare means of two groups of data but only with two...

03 March 2021 8,796 3 View

Enhanced Yellow Fluorescent Protein (Aequorea victoria) DNA sequence?

I am on the lookout for the Enhanced Yellow Fluorescent Protein (Aequorea victoria) DNA sequence. Does anyone know where I can find it? Thank you in advance

03 March 2021 3,568 1 View

What kind of fluid could I use for a pitfall trap that also does not invalidate molecular testing?

Hi, I want to start testing pitfall trap to obtain ants samples, but I need to conduct molecular analysis on those insects. So, what kind of fluid can I use? Ethanol expires too early and I need...

03 March 2021 5,978 5 View

What's the best way to measure growth rates in House sparrow chicks from day 2 to day 10?

What's the best way to measure growth rates in House sparrow chicks from day 2 to day 10? Since, the growth curve from day 2 to 10 won't be like the "Logistic curve" it might not follow logistic...

03 March 2021 1,401 3 View

I got 02 moderator values defining Johnson-Neyman significance regions. Is it an error?

Hi everyone, I am conducting research for my Master's thesis. I am using PROCESS by Johnson-Neyman to analyze my Moderator model. I test the relationship between Public Service Motivation and...

03 March 2021 2,350 2 View

Do we need to write protocol for a second study of a systematic review that has been registered and published?

I have conducted and published a systematic review and meta-analysis research with the topic related to public health and health pomotion (protocol was registed in PROSPERO). Now we want to...

03 March 2021 8,920 3 View

Michael Tordoff Popular answer

The Mann-Whitney and Wilcoxon tests are rank sum tests, not median tests. It is quite possible for the ranks to differ but the medians to be the same. This website has a nice example...

http://www.ats.ucla.edu/stat/mult_pkg/faq/general/mann-whitney.htm

Michael Tordoff

Fathi M Sherif

As far as I know, both tests are used for non-parametric data (not normally distributed) or for groups with very low numbers for the first test and larger number of samples for the second. The first test is used to see difference between iwo unmatched samples whereas the second test to see the dufference between two matched samples and larger number of samples. So difference in number of samples sometimes gives same median but sure with different standard error and standard deviation. It is always very wrong to express your data with only mean or median without Standard error or diviation.

Saleh Ameer

Dear Brijesh,

If two groups have an identical or similar distribution of scores shape AND have identical medians then you can be sure that there is no significant difference between them. However, if they have equal medians but different distribution shapes then it is not uncommon to find a significant difference.